Summary of Significant Accounting Policies - Additional Information (Details)					12 Months Ended
		Sep. 25, 2018 USD ($)	Feb. 16, 2018 USD ($)	Jan. 12, 2017 USD ($)	Dec. 31, 2018 USD ($) Instrument	Dec. 31, 2017 USD ($) Instrument	Dec. 31, 2016 USD ($) Instrument	Jan. 01, 2018 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Deferred revenue, revenue recognized					$ 83,300,000	$ 76,400,000	$ 72,000,000
Deferred commissions, amortization period					4 years			4 years
Amortization of deferred commissions					$ 1,600,000	1,000,000	500,000
Impairment loss related to deferred commissions					0	0	0
Cumulative amount of unrecognized stock-based compensation expense recognized		$ 89,900,000			131,770,000	34,986,000	32,957,000
Remaining unamortized stock-based compensation					$ 27,600,000
Remaining weighted-average requisite service periods					1 year 6 months
Impairment of long-lived assets						0
Intangible assets, derecognized							3,700,000
Impairment of property and equipment					$ 2,821,000	0	0
Impairment of goodwill					0	0
Goodwill, derecognized							12,182,000
Currency translation adjustment upon subsidiary liquidation					0	0	1,397,000
Private company investment					3,600,000	$ 3,600,000	$ 5,000,000
Impairments on private company investment					0
Observable price changes for private company investment					$ 0
Derivative financial instruments | Instrument					0	0	0
Deferred rent balance					$ 7,500,000	$ 4,800,000
Liability for sabbatical leave, accrued balance					4,400,000	3,600,000
Advertising and promotion costs					24,000,000	17,600,000	$ 13,600,000
Cash consideration from sale of private company investment				$ 11,700,000
Gain on sale of private company investment					$ 999,000	6,750,000	0
Sale of private company investment, period of contingent consideration to be received					3 years
Earn-out payment received			$ 1,000,000
Sales and marketing expense	[1],[2]				$ 95,783,000	73,511,000	73,970,000
Total assets					679,348,000	578,089,000
Adjustments of retained earnings					(332,268,000)	(177,571,000)
Accounting Standards Update 2018-07
Summary Of Significant Accounting Policies [Line Items]
Adjustments of retained earnings								$ (43,000)
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Summary Of Significant Accounting Policies [Line Items]
Sales and marketing expense						(1,000,000)	$ (900,000)
Total assets						3,200,000
Accrued Expenses And Other Current Liabilities
Summary Of Significant Accounting Policies [Line Items]
Deferred rent balance					300,000	200,000
Other Non-Current Liabilities
Summary Of Significant Accounting Policies [Line Items]
Deferred rent balance					7,200,000	4,600,000
Liability for sabbatical leave, accrued balance					2,100,000	1,900,000
Accrued Compensation
Summary Of Significant Accounting Policies [Line Items]
Liability for sabbatical leave, accrued balance					$ 2,300,000	$ 1,700,000
Capitalized Internal-Use Software
Summary Of Significant Accounting Policies [Line Items]
Intangible assets estimated useful life					3 years
Customer Concentration Risk | Sales Revenue, Net
Summary Of Significant Accounting Policies [Line Items]
Concentration of credit risk, customer					No single customer accounted for more than 10% of revenue	No single customer accounted for more than 10% of revenue	No single customer accounted for more than 10% of revenue
Customer Concentration Risk | Accounts Receivable
Summary Of Significant Accounting Policies [Line Items]
Concentration of credit risk, customer					No customers accounted for more than 10% of accounts receivable, net	No customers accounted for more than 10% of accounts receivable, net
Other Non-Operating Income (Expense)
Summary Of Significant Accounting Policies [Line Items]
Currency translation adjustment upon subsidiary liquidation							$ (1,400,000)
Out-of-the-Money Stock Option and At-the-Money Stock Option
Summary Of Significant Accounting Policies [Line Items]
Share-based compensation, fair value assumptions, expected dividend rate					0.00%
Equity Incentive Plans | Time-Based Awards | New Hires
Summary Of Significant Accounting Policies [Line Items]
Stock-based compensation, requisite service period					4 years
Equity Incentive Plans | Time-Based Awards | Existing Employees
Summary Of Significant Accounting Policies [Line Items]
Stock-based compensation, requisite service period					3 years

[1] Includes amortization of acquisition intangible assets as follows: Year Ended December 31, (in thousands) 2018 2017 2016 Cost of revenue $1,952 $2,040 $4,505 Sales and marketing 2,318 2,421 4,267 Amortization of acquisition intangible assets $4,270 $4,461 $8,772

[2] Includes stock-based compensation, net of amounts capitalized as follows: Year Ended December 31, (in thousands) 2018 2017 2016 Cost of revenue $8,931 $2,503 $4,114 Research and development 48,739 9,918 5,756 Sales and marketing 19,046 8,069 8,712 General and administrative 55,054 14,496 12,301 Restructuring — — 2,074 Stock-based compensation, net of amounts capitalized $131,770 $34,986 $32,957